US2145815A - Zinc sulphide pigment - Google Patents

Description

OR 211 59815 SR Patented Jan. 31, 1939 UNITED STATES oearcn i188.

PATENT OFFICE ZINC SULPHIDE PIGMENT No Drawing.

Application March 17, 1937,

Serial No. 131,405

14 Claims. (Cl. 23-135) .This invention relates to a method for the production of zinc sulphide pigment and to the misstatement twinned- This application is a continuation in part of my copending application, Ser. No. 22,583, filed product of low hiding-power; the alkalinity of the 5 May 21, 1935. solution eliminates deterioration of equipment The process of this invention involves the preand contamination of materials therein; the gencipitation of zinc sulphide, as by means of hyeral procedure, especially in the co-ordination of drogen sulphide, from an amino-zinc salt solusuch factors as the concentration of ammonia tion; and such procedure possesses valuable and zinc in the solution, the temperature and 10 technical and commercial advantages, but comagitation of the solution, the concentration of mercial zinc sulphide pigment has not heretothe hydrogen sulphide in the gas, and the time fore been produced by any process involving such of the precipitation, is such that it produces with procedure. Commercial zinc sulphide pigment simplicity and certainty the superior final product now and heretofore available has been precipiof the invention and the precipitate having the 16 tated from an acid solution and numerous dimproperties above mentioned; and the by-products, culties in that procedure and deficiencies in the ammonia salts, are valuable and in readily reproduct thereof are avoided in the practice of coverable form. Moreover, the requirements in this invention. respect of the hydrogen sulphide gas are such White pigments must possess such physical that cheap supplies may be used, and the require- 20 characteristics that they will meet very exacting ments in respect of the zinc are such that zinc requirements and the process and product of skimmings from galvanizing plants and zincifthis invention are such that the zinc sulphide erous flue dusts from secondary copper blast furpigment thereof possesses superior color or whitenaces may readily be employed in the production ness, superior coloror tinting-strength, high of zinc salt solution. 25 hiding power, inherent resistance to the darken- In the practice of this invention the precipiing action of light and especially the ultra violet tate is recovered from the solution by filtration, rays thereof, unusual and advantageous alkalinwashed, dried, calcined, quenched, milled, dried ity, qispersabilityin eit ggrlater or oil without\ and disintegrated to produce the final zinc sulspecial surface treatment, superior chemical purphide pigment oi the invention. However, the ity, superior behavior when embodied in paint )intermediate product, consisting of the washed having an oil or varnish vehicle, and other valuprecipitate, after drying and milling, if necesable properties. Certain of these properties are sary, is a valuable product both as being especially due to the suitability and uniformity of the partiwell suited to the subsequent steps for the procle size, the purity, and the dispersability of th duction of a final zinc sulphide pigment and as a final product which result from the advantageous pigment in priming coats. This intermediat 1 features of the process. Advantages of the proc-{ product has uniform and suitable article size ess are that the zinc sulphide precipitate requires and contains high proportion, 2 0 to 2.5%, no end pointing or alkalizing, requires no agof. ammonia even though dried to a constant ing, is readily filterable, is of such uniform and weight at 120 C. These properties cause the 40 suitable particle size and possesses such content intermediate uncalcined product to inhibit corof ammonia that it is valuable as a corrosion? s pj to p s ss hid -p wrshfllcf nt fo resistant primer without calcining and milling a'p'flming coat and about equal to that of zinc and is especially suited to calcining without oxoxide, and tinting strength substantially equal to idation to produce the superior final product, is that of lithopone. readily washable, produces a coherent filter cake 'Other and further advantages and features of that is not slimy nor impervious nor chalky, and this invention will appear from the following decalcines to produce a readily millable product scription of an illustrative operation of the procthat is not hard nor horn-like but yields a final ess and from the description of the intermediate product having the above-mentioned properties; and final products thereof. the solution from which the precipitate is formed The solution from which the crude zinc sulcarries a high concentration of zinc and the size phide is precipitated is a purified zinc salt soluof the equipment is thereby minimized; the high tion in which the salt is preferably a nitrate concentration of zinc and the conditions probut may be a sulphate or chloride. The solumoting solution of hydrogen sulphide result in a tion should be substantially free of elements,

rapidity of precipitation that greatly reduces the time involved and minimizes the possibility of producing a challw precipitate that makes calcining. difilcult and leads to a yellow calcined .oxide gas, .or other suitable'diluent gas.

other than Ni, which form insoluble sulphides, e. g., Mn, Cu, Cd, Pb, Fe, Sn, Sb, As, etc., but it may contain Ni, 8, a d .KDQGQL SQ may form an insoluble sulphide and the conditions maintained in the operation of the process prevent that from being precipitated although in the acid process any Ni would be quantitatively precipitated and impair the light resistance and perhaps the permanent color of the resulting zinc sulphide. Preferably the zinc isimtheiorm ofaau ammino zinc salthsuclnas ammino-zinc nitrate Zn(NHa)4(NOa) 1, It is usually in that form as a result of the operations involved in the preparation and purification of the solution, but in any event, the solution is saturated with ammonia before precipitation is started. The solution preferably has a zinc concentration of about 160 grams to 200 grams of Zn per liter, and preferably about 180 grams of zinc per liter. Below that range close adjustment of other factors is necessary to obtain a calcined product sumciently free of yellow color, although an analysis of such a yellow product does not indicate that that color is due to the presence of zinc oxide. Concentrations above 200 grams of Zn per liter cause the resulting slurry to be too thick for the dispersion of gas therein, and may lead to a yellow color in the calcined product possibly due to the presence of undesirable zinc compounds formed because the thickness of the slurry prevented complete reaction.

At all times during the precipitating step the temperature is maintained at about 50 C. to 80 C. and preferably in the neighborhood of 70 C. by such addition or removal of heat as may be necessary, the reaction being exothermic. At temperatures below about 50 C. the precipitate tends to be too fine for eiiicient (rapid and complete) filtration and washing. At temperatures above about 80 C. the solution holds too little ammonia in solution, with the consequences hereinafter set out. The relatively high temperature employed prevents the absorption in the solution of CO2 or HCN that may be in the gas fed thereto and therefore minimizes the formation of carbonates and cyanides. Such temperature facilitates the attainment of advantageous particle size in the precipitate.

To the solution having the properties and being in the condition above stated, ammonia gas is supplied below the surface in such quantity and at such time or times as not only to insure saturation of the solution by ammonia prior to the addition of hydrogen sulphide but to insure, throughout the precipitation step, high ammonia concentration or saturation or even an excess, in spite of the relatively high temperature of the solution and the "sweeping-out tendency by other gases. Ordinarily ammonia will be so supplied throughout the precipitation to maintain this condition.

To the solution, saturated with ammonia, hydrogen sulphide gas is fed below the surface thereof, preferably accompaniedbycarbon di- Ordinarily V to 1 volume of ammonia is fed to the solution during precipitation for each volume of Has. The mixture of H23 and CO2, or other diluent gas, preferably contains 25% or more of HzS, 75% of H2S having been found to be highly effective, and 100% of His having been found to produce a lack of brightness or dullness in the paint in which the pigment is embodied. If the ercentage of CO2, or other diluent gas, is more than 50% of the mixture it may be desirable to increase the proportion of ammonia above the range stated to compensate for that swept out by the diluent gas and so maintain high concentration or saturation of the solution by ammonia.

Maintaining the temperature of the solution as above stated, the solution is agitated sufficiently to prevent settling of the precipitate to the bottom of the vessel, but the agitation is not so intense as to give a highly hydrated fine precipitate that is too fine to filter and horny when dried. Insufilcient agitation causes the calcined product to have a yellow color presumably due to incomplete reaction upon solution entrapped in settled precipitate. Thus, although higher solution temperatures require special precautions to maintain proper ammonia content in the solution, it is only by maintaining such higher temperatures which tend to produce a coarser precipitate that it is possible to employ sufllcient agitation to prevent undesirable yellowness of the product.

The gas employed should be freed of tar and organic compounds of all classes and preferably all cyanides and carbon bisulphide.

The maintaining of saturation of the solution by ammonia is highly important in the attainment of the advantages of the invention. If not maintained, the precipitate will either be so fine and slimy as to prevent filtration and washing or will give a slimy cake that becomes horn-like, hard and translucent upon drying and cannot be calcined or milled to produce a pigment. Since the ammonia supply must be at a rate sufiicient to maintain high concentration or saturation, in spite of the relatively high temperature of the solution and in spite of the sweeping-out" action of other gases fed to the solution, and especially diluent gas, the advantages of the invention cannot be achieved by the use of coke oven gas as a supply of hydrogen sulphide because those gases contain only about 0.5% by volume of H23 and less 1% of NH3, and the feeding of enough gas to provide the necessary HzS results in the sweeping out of the solution, when at its proper temperature, all NH: except such small percentage as might remain present as a result of reaching equilibrium with the coke oven gas which contains such a low percentage of M13. Moreover, coke oven gas could not be sumciently freed economically of all organic compounds to give white pigment. Saturation or high concentra tion of NH: in the solution, in spite of the relatively high temperature thereof, prevents coprecipitation of Zn (OH): (and basic zinc salts in general, e. g., basic zinc carbonate), whereas precipitation thereof is promoted in the presence of a small amount of ammonia, the presence of zinc hydroxide or such basic zinc salts in the precipitate causing it to be fine and causing the filter cake to be slimy and incapable of being efliciently washed. This causes the dried filter cake to be horn-like and incapable of being converted into suitable pigment by calcination and milling. Moreover, the zinc hydroxide or basic zinc salts would appear in the calcined product as zinc oxide and would impart yellow color to the pigment. Saturation by, or excess of, ammonia in the solution at such temperature as gives a proper rate of precipitation and proper coarseness of precipitate also prevents zinc cyanide and zinc carbonate from forming, although zinc carbonate could form in the absence of such quantity of ammonia at the temperature emcnnmsmy,

ployed. This is important because zinc carbonate and zinc cyanide cannot be converted completely to sulphides unless an excess of 1118 be used and such excess is avoided in the invention. Although the use of the relatively high temperature necessitates continual and ample supply of ammonia, it opposes the formation of ammonium carbonate that would clog the system and use up ammonia.

A very important advantage oi the high con centration of ammonia is that it facilitates the absorption of hydrogen sulphide, which usually does not escape from the surface of the solution, it being possible that the sulphur is passed to the zinc through an ammonium sulphide stage.

Care is taken to avoid the introduction of an excess of hydrogen sulphide, as by applying some of the slurry to lead acetate indicator paper to observe any soluble sulphide ion. Avoidance of such excess is important to the avoidance. of polysulphides of ammonia, and perhaps of zinc. The polysulphides of ammonia, although soluble, do not appear to wash out of the precipitate and all polysulphides impart yellow color to the pigment. Moreover, in the recovery of by-product ammonia salts the removal oi sulphur is troublesome.

Due to the conditions above described, the precipitation is rapid and is usually complete in one to two hours. Such failure to maintain the conditions above described as leads to a precipitation time of four or more hours results in definite degradation oi the product, and the filter cake becomes chalky and disintegrates into powder in preparing it for and passing it through the calcining operation, and a yellow product results even though analysis may not show unusually high oxygen content, and, also, the final product lacks tinting strength because of non-uniformity and excessive range of particle size.

By maintaining conditions as above described the precipitation of zinc is quantitative and the final pigment will comprise more than 99% zinc sulphide. As contrasted with this advantage, precipitation from an acid solution, as in the Myhren et al. Patent No. 2,020,902, requires that the solution be relatively dilute, containing about 30 grams Zn per liter, to prevent solution of zinc sulphide in the resulting acid and even then the slurry contains as much as 1.5 gr. per liter of unprecipitated Zn (5% of the original zinc) and 4.5% of sulphuric acid. The recovery of values from such mother liquor presents great dim.- culties. Attempts to avoid such difllculties and increase precipitation of zinc sulphide by addition of barium sulphide have been ineffectual because it has been impossible so to decrease the acidity to any substantial extent and produce pigment that is within the specification of 97% ZnS content for zinc sulphide pigment. In the acid process, as in Stutz et al., No. 2,020,918, "end pointing of the precipitate, consisting in repulping the washed pigment and adding alkaline compounds, such as barium or calcium hydroxide, has to be applied to the precipitate to render it alkaline, and further contamination of the product results.

In the precipitation of zinc sulphide from an' QEEFCQ at once be separated by filtration and readily washed to a content of less than 0.2% of ammonia salts and will produce a coherent filter cake that will not disintegrate into dust or become horn-like and useless when dried. When salts in the solution are nitrates, advantages are that they have higher solubility than other salts and are therefore more readily kept in solution and washed from the precipitate, and such residue of salts as remains in the filter cake exerts in the calcining a slight oxidizing, effect that removes any carbon due to the presence of traces of organic matter. 'IlllLZiXlLSlllQbliQlH he. washed filtgrcalgecontainszrdtglfi of ammonia which is 9Lwashed-eut-and whicifis'fiot'removed in drying the cake to constant weight at 120 C. The zinc sulphideflin the dried cake constitutes the aliiable. intermediate productbf. this invention, and it not only constitutes a material that is especially suitable for subsequent treatment for production of the final zinc sulphide pigment of this invention, but constitutes a material which, due to its content of ammonia, its corrosioninhibiting power, its uniform and suitable particle size and its covering power, is highly valuable as an ingredient of a priming paint. This intermediate product is dried, usually in the atmosphere at about 100 C. If used as a primer pigment it is rissliszamletatwmsliitconmins substantially @gee moisture and disintegrated. Iipasse'd on to califiatl'omit' is advantageously dried to a moisture content of 15% to 20%.

To produce zinc sulphide pigment in its final form from the partly dried filter cake (containing about 15% of water), the cake is broken into small particles having an average dimension of about A", calcined at 650-'780 C. in an inert atmosphere such as superheated steam in the usual manner to drive of! free water and water of hydration and ammonia, and to expand the particles to such size that they effect that dispersion of light which gives the pigment hiding or covering power, quenched in water, milled in a ball mill, dried, and disintegrated, as in a cage I mill, into dry pigment.

The zinc sulphide pigment of this invention possesses distinctive properties.

The product, free of cobalt, possesses light resistance (resistance to darkening when subjected to light while wet) equal to or better than the light resistance possessed by present commercial zinc sulphide pigment that contains cobalt, in accordance with the teaching of the Jantsch and Wollski Patent No. 1,693,902, for the improvement of the light resistance thereof. The product p sscse.such.1i ntrei sea. spimlflfi fist that it may contain as much as 0.4% or more of chlorine by reason of having been produced from zinc chloride salt. The quality or superiority of the light resistance of this product over the light resistance of the commercial zinc sulphide pigment was proved by the Breyer, Nelson & Farber method described in Physical and Chemical Examination of Paints, Varnishes, Lacquers and Colors" by H. A. Gardner, 7th Edition, 1935, page 226, using as a vehicle dammar-turpentine mixture or linseed oil. The reason for this advantageous property cannot be wholly explained. It may be due to the fact that the product of this invention possesses such chemical purity (more than 99% zinc sulphide, dry basis) that the impurity thereof can only be determined by spectroscopic analysis. In contrast the A. S. T. M. Standard of 1936, No. D386-86 for pure zinc sulphide pigment is only 97% ZnS.

herent alkalinity such that gment-in-watexagiyes 141E ygue in the rapgflfl to lfllk This inherent alkalinity in conjunction with the high (more than 99% on a dry basis) content of ZnS is unique and. in sharp contrast with the product precipitated from an acid solution especially after end-pointing thereof above mentioned, and in sharp contrast with present commercial pure zinc sulphide pigment. It being economically impossible to avoid some occurrence of ZnO in the calcined final product in commercial operation of the process of this invention, it is significant that the content of ZnS plus ZnO (dry basis) of the product of this invention when the process is operated with intelligent care is as high as 99.9% and it still has the alkalinity above mentioned.

The high purity of the finished calcined and milled zinc sulphide pigment is indicated by the following values, in percent on the zinc, obtained Total metals other than Zn .0074 to .0146% Total alkali and alkali earth metals .0030 to .0085% The indication not identifiable means that the characteristic line or lines could not be identified on the spectroscope.

The foregoing values indicate a zinc purity of 99.9926% to 99.9854%.

The desirable alkalinity of the pigment of this invention, pH 8 to 9, is remarkable in view of the low content of alkali and alkali earth metals, and is possibly due to the presence of ammonia throughout the precipitation, the high ammonia content of the precipitate, the nature of the association of that ammonia with the precipitate, and the presence of that ammonia during the calcining operation. The low content of alkali and alkali earth metals, especially barium and calcium, is due to the complete omission of "end pointing of the precipitate. The absence of cobalt is due to the superior light resistance of the pigment which eliminates the necessity for adding cobalt. The low content of aluminum and sodium is due to the high whiteness of the product which eliminates or minimizes the necessity for adding ultramarine blue.

The product has high tinting strength as compared to commercial zinc sulphide pigment. Three grams of the product oi this invention gave no darker final shade when mixed with 0.3 gram of ultramarine blue than did three and one-half grams of Cryptone ZS20 which is marketed as pure zinc sulphide pigment.

The product has superior dispersability characteristics. When the product is utilized in enamel having a varnish vehicle the leveling or disappearance of brush marks is almost com- The finished pigment is of an 111-.

plete, whereas the same quantity of commercial pigment in the same quantity of the same varnish leaves definite brush marks. It is importantthat the pigment is dispersable in either oil or water and can be used in kalsomine and casein 5 coating compounds without the surface treatment (e. g. soap) necessary in connection with commercial zinc sulphide pigments. The prod uct has such whiteness and brightness that its color can be made to match the artificial bluewhiteness of commercial zinc sulphide pigment that is due to addition of ultramarine blue, by adding so little ultramarine blue that the brightness is not seriously lowered and remains substantially above that of standard commercial zinc sulphide pigment. There is no test for the demonstration of this property that is as good as using the unaided eye in the comparison of samples of pigment worked out in the same vehicle and smeared on one surface of glass and compared through the other surface of the glass.

The solution from which the zinc sulphide is precipitated contains substantial quantities of free ammonia. To recover the same, the filtrate from the zinc sulphide is passed through an ammonia stripping column, where the solution is heated and the ammonia is driven off and recovered in any suitable manner, e. g., by solutio in zinc nitrate solution, by neutralization wit sulphuric acid to form ammonium sulphate, etc. The stripped solution then comprises a concentrated solution of ammonium nitrate, which is simply evaporated and crystallized to produce solid ammonium nitrate, suitable for use in the manufacture of explosives, etc. The dilute sulphuric acid by-product of precipitation from an acid solution is practically valueless.

The zinc salt in the solution from which the precipitate is formed may be a sulphate or a I chloride instead of being a nitrate, but when the 40 salt is a chloride the washing of the filter cake to reduce the salt content thereof should be carried out by using ammonium hydroxide for at least the first washing. This is because the filter cake obtained from the solution of chloride contains some zinc salts which are soluble in the presence of ammonia, but if the ammonia is washed out by washing with water, these salts precipitate as zinc oxychlorides which impair the light resistance of the pigment. By washing the filter cake with ammonium hydroxide precipitation of these salts as oxychlorides is avoided and they are washed out and the superior light resistance of the product is assured.

From the foregoing it will be apparent that the process of this invention efiects the production of pure andvaluable zinc sulphide pigment and that the process is simple and effective in that the precipitation of cyanides, basic zinc carbonates and polysulphides and other troublesome compounds is prevented and the precipitate is in handleable form and pure, and especially is in a form in which it may be used at once with great advantage or converted to a final pigment form by calcining and milling, the high content of adsorbed ammonia contributing to the superior qualities of the intermediate product, cooperating in the calcining to protect and improved the calcined product, and causing the final product to be alkaline but uncontaminated.

I claim:

1. In a method for the production of zinc sulphide pigment wherein zinc sulphide is precipitated from zinc salt solution by gas containing hydrogen sulphide, the steps comprising precipi- 23. cnnmsmv'.

leg [U tating the zinc sulphide from a solution initially containing approximately 160 grams to approximately 200 grams of Zn per liter and maintaining such concentration of ammonia therein as will prevent substantial precipitation of zinc hydroxide and produce a readily filterable precipitate.

2. In a method for the production of zinc sul-.

phide pigment wherein zinc sulphide is prec ipitated from ammino zinc salt solution b gas containing hydrogen sulphide, the steps comprising precipitating the zinc sulphide from a solution initially containing approximately 160 grams to approximately 200 grams of Zn per liter, while maintaining such concentration of ammonia therein as will present substantial precipitation of zinc hydroxide and subjecting the solution to such agitation as will prevent substantial settling of the zinc sulphide precipitate.

3. An intermediate product in the production 0g zinc sulphide pigment by precipitation from an ammino-zonic salt solution, comprising substantially white uncalcined dried zinc sulphide precipitate containing 2.0% to 2.5% of ammonia.

4. In a method for the production of zinc sulphide pigment wherein zinc sulphide is precipitated from ammino-zinc salt solution by gas containing hydrogen sulphide, the steps comprising precipitating the zinc sulphide from a solution initially containing approximately 160 grams to approximately 200 grams of Zn per liter while maintaining the solution at a temperature of about 50 C. to C. and while maintaining such concentration of ammonia therein as will prevent substantial precipitation of zinc hydroxide, and subjecting said solution during precipitation to such agitation as will prevent substantial settling of the precipitate and produce uniform particle size oi! the zinc sulphide precipitate.

5. In a method for the production of zinc sulphide pigment the step comprising, precipitating zinc sulphide from an ammino-zinc salt solution with a gas containing hydrogen sulphide while maintaining in said solution during precipitation such concentration of ammonia as will prevent substantial precipitation of zinc hydroxide therein.

6. In a method for the production of zinc sulphide pigment the step comprising, precipitating zinc sulphide from an ammino-zinc salt solution with a gas containing hydrogen sulphide while maintaining said solution substantially saturated with ammonia substantially throughout the precipitation of said zinc sulphide.

7. In a method for the production of zinc sulphide pigment the steps comprising, substantially saturating an ammino-zinc salt solution with ammonia, and precipitating zinc sulphide from search said ammonia saturated solution with a gas containing hydrogen sulphide while maintaining subticom stantial ammonia saturation in the said solution throughout the precipitation oi! said zinc sulphide.

8. The method of claim 6 in which the ammino-zinc salt solution is maintained at a temperature of about 50 C. to 80 C. throughout the precipitation of said zincsulphide.

9. The method of claim 5 in which the ammino-zinc salt solution throughout the precipitation step is subjected to such mild agitation as will prevent substantial settling of the zinc sulphide precipitate, prevent a highly hydrated fine precipitate that is too fine to filter and horny when dried and prevent entrapping of unreacted solution in settled precipitate.

10. The method of claim 5 in which the ammino-zinc salt solution is maintained at a temperature of about 50 C. to 80 C. throughout the precipitation of said zinc sulphide.

11. In a method for the production of zinc sulphide pigment the steps comprising, precipitating zinc sulphide from an ammino-zinc salt solution with a gas containing hydrogen sulphide while maintaining such concentration of ammonia in said solution as will prevent substantial precipitation of zinc hydroxide and maintaining the said solution at a temperature of about 50 C. to 80 C., and agitating said solution during the precipitation to prevent substantial settling of the zinc sulphide precipitate.

12. In a method for the production of zinc sulphide pigment the steps comprising precipitating zinc sulphide from an ammino-zinc salt solution with a gas containing hydrogen sulphide while maintaining in said solution during precipitation such concentration of ammonia as that the zinc sulphide precipitated will contain 2.0% to 2.5% of adsorbed ammonia that is not removable by washing and drying, washing and drying the precipitate, and calcining the dried precipitate that contains substantially all or said ammonia.

13. The method of claim 5 in which the zinc sulphide is precipitated from an ammino-zinc chloride solution followed by the step of washing the zinc sulphide so precipitated in the presence of ammonia.

14. The method of claim 5 in which the zinc sulphide is precipitated from an ammino-zinc nitrate solution, and the additional step of agitating the said solution during the precipitation to prevent substantially settling of the zinc sulphide precipitate, to prevent a highly hydrated fine zinc sulphide precipitate that is too flne to filter and horny when dried, and to prevent entrapping of unreacted solution in settled zinc sulphide precipitate.

DONALD G. MORROW.

g t .1: /j5biRTIFIcATE OF CORRECTION.

Patent No. 2,1L 5, 15. Januar 31, 19 9.

' DONALD G. noRRow 1 It is hereby certified that error appears in the printed specification of the above numbered p'atent requiring correction ae followeg Page 2, second column, line 1 1 after "less" insert than; beige}, second column, line 71;, for "D386-86" read 13386 -56; page 5, first column, line 16, claim 2, for the word "present" read prevent; line 21;c1a1m5, for "o3" read of; and line 22,- aame claim, for "aminc-zonic" read amino-zinc; same page, second column, line 5b., claim 11 for the word "substantially" read substantial; and that the said Letters Patent should be read with this correction therein that the same may conform to therecord of the case in the Patent Office.

Signed and sealed this hth day of-April, A. D. 1959.

Henry Van Arsdale (Seal) Acting Caimnztssioner of Patents